The present invention relates in general to a data processing apparatus incorporating a decimal arithmetic function. In particular, the invention concerns detection of overflow in the data processing apparatus which is adapted for performing decimal arithmetic operations with the aid of a decimal arithmetic unit having an operation width corresponding to a plurality of bytes.
Heretofore, arithmetic units operative on the byte base have been extensively employed as a means for implementing decimal arithmetic functions. In this connection, detection of overflow is effected serially for every byte, involving substantially no technical problems.
However, recently with the advent and development of the decimal arithmetic unit having an operation width (or capacity) corresponding to a plurality of bytes, the presence or absence of an overflow in the result of the decimal arithmetic operation is detected in succession to the execution of the arithmetic operation cycle by verifying whether a binary "1" is set or not at a more significant position than that of the byte which has undergone the decimal arithmetic operation. To this end, there is employed a shifter or the like. This system requires, however, an additional cycle for detecting the overflow after the arithmetic operation cycle. This means that the speed of the decimal arithmetic operation is correspondingly lowered, providing a problem to be solved for enhancing the performance of data processing apparatus incorporating the decimal arithmetic unit of the plural byte capacity.